import java.lang.String;
import java.util.HashSet;

public class One {
    public static void main(String[] args) {
        if (args.length <= 0)
            return;

        if (allDifferentChar3(args[0])) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
    }

    private static boolean allDifferentChar(String str) {
        HashSet<Character> hs = new HashSet<Character>();
        for (int i = 0; i < str.length(); ++i) {
            char c = str.charAt(i);
            Character ch = new Character(c);
            if (hs.contains(ch)) {
                return false;
            } else {
                hs.add(ch);
            }
        }
        return true;
    }

    private static boolean allDifferentChar2(String str) {
        if (str.length() > 256)
            return false;

        boolean[] data = new boolean[256];
        for (int i = 0; i < str.length(); ++i) {
            if (data[str.charAt(i)])
                return false;
            else
                data[str.charAt(i)] = true;
        }

        return true;
    }

    private static boolean allDifferentChar3(String str) {
        if (str.length() > 26)
            return false;

        int data = 0;
        for (int i = 0; i < str.length(); ++i) {
            if ((data & (1 << (str.charAt(i) - 'a'))) != 0)
                return false;
            data |= 1 << (str.charAt(i) - 'a');
        }

        return true;
    }
}
